1. Field of the Invention
The present invention relates to input devices and electronic devices, more particularly, to an input device and an electronic device that generate a signal corresponding to a position depressed on their input domains.
Recently, the expanding market for information communication apparatuses and terminal units in business use has rapidly increased the demand for touch panels. A touch panel is incorporated suitably in a small apparatus such as a PDA (personal digital assistant), because it is arranged in a stack together with a display device and can be satisfactorily operated on the display device. Among types of touch panels, there has been a stronger demand for a resistance film type touch panel, which is capable of controlling and operating easily not only PDAs but also office computers and personal computers. Normally, a touch panel is arranged on the surface of a display device, and is incorporated so that it can operate together with what is projected on the display device. Here, it is required that relative positions of the touch panel and the display device be accurately aligned. Thus, correcting an input coordinate of the touch panel on the basis of the relative position of the touch panel to the display device, that is, calibration, is usually carried out.
2. Description of the Related Art
FIG. 1 illustrates a structure of a system incorporating an input device with a resistance film type touch panel.
An input device 1 is placed on a screen 3 of a display device 2. Icons, buttons and so on are projected on the screen 3 of the display device 2. Depressing positions corresponding to the icons and the buttons projected on the screen 3 of the input device 1 starts applications corresponding to the icons and the buttons.
The input device 1 comprises a touch panel 11 and an interface circuit substrate 12.
FIG. 2 is an exploded perspective view of the touch panel 11.
The resistance film type touch panel 11 is constructed in a stack together with a lower substrate 21 and an upper substrate 22 by putting dot spacers, which are not illustrated, between the lower substrate 21 and the upper substrate 22. A flexible wiring board 4 to be connected with the interface circuit substrate 12 is glued to an edge between the lower substrate 21 and the upper substrate 22.
The lower substrate 21 comprises a glass substrate 31, a conductive film 32, electrodes 33 and 34, and wiring patterns 35 through 38. The conductive film 32 is formed of a transparent conductive material such as ITO (indium tin oxide), and is set on the glass board 31.
The electrode 33 is formed of a conductive material such as aluminum, and is shaped in the form of a straight line on an edge of the conductive film 32 in the arrow X1 direction. The electrode 34 is formed of a conductive material such as aluminum, and is shaped in the form of a straight line on an edge of the conductive film 32 in the arrow X2 direction. The electrodes 33 and 34 are formed in parallel.
The wiring pattern 35 is connected with the electrode 33 at its one end, and with a wiring pattern 51 on a flexible wiring board 23 at the other end. The wiring pattern 36 is connected with the electrode 34 at its one end, and with a wiring pattern 52 on the flexible wiring board 23 at the other end. As mentioned above, both the electrodes 33 and 34 are connected with the interface circuit substrate 12. Also, the wiring pattern 37 is connected with a wiring pattern 53 on the flexible wiring board 23, and the wiring pattern 38 is connected with a wiring pattern 54 on the flexible wiring board 23.
The upper substrate 22 comprises a film 41, a conductive film 42, electrodes 43 and 44, and wiring patterns 45 and 46. The film 41 is formed of synthetic resin such as PET (poly-ethylene-telephtalete) shaped in the form of a film, and has flexibility. The conductive film 42 is formed of a transparent conductive material such as TTO (indium tin oxide), and is set on the under surface of the film 41 toward the lower substrate 21.
The electrode 43 is formed of a conductive material such as aluminum, and is shaped in the form of a straight line on an edge of the conductive film 42 in the arrow Y1 direction. The electrode 44 is formed of a conductive material such as aluminum, and is shaped in the form of a straight line on an edge of the conductive film 42 in the arrow Y2 direction. The electrodes 43 and 44 are formed in parallel.
The wiring pattern 45 is connected with the electrode 43 at its one ends and with the wiring pattern 53 on the flexible wiring board 23 at the other end through the wiring pattern 37 on the lower substrate 21. The wiring pattern 46 is connected with the electrode 44 at its one end, and with the wiring pattern 54 on the flexible wiring board 23 at the other end through the wiring pattern 38 on the lower substrate 21. The electrodes 43 and 44 are connected with the interface circuit substrate 12 through the flexible wiring board 23.
Dot spacers are formed of an insulator such as resin, and are placed between the lower substrate 21 and the upper substrate 22. While there is no depressing action, the dot spacers prevent contact between the conductive film 32 on the lower substrate 21 and the conductive film 42 on the upper substrate 22.
When the upper substrate 22 is depressed, the upper substrate 22 bends and the conductive film 42 on the upper substrate 22 touches the conductive film 32 on the lower substrate 21. The contact of the conductive film 42 on the upper substrate 22 and the conductive film 32 on the lower substrate 21 provides coordinates of the contact point that can be detected.
An explanation of a series of actions for detecting the coordinate will now be given.
The interface circuit substrate 12 repeatedly alternates between the following two actions. One action is to apply a predetermined voltage of Vcc between the electrodes 33 and 34 formed on the lower substrate 21 and to detect an electric potential of the electrode 43 of the upper substrate 22. The other action is to apply a predetermined voltage of Vcc between the electrodes 43 and 44 formed on the upper substrate 22 and to detect an electric potential of the electrode 33 on the lower substrate 21.
If the predetermined voltage of Vcc between the electrodes 33 and 34 formed on the lower substrate 21 is applied, a potential gradient between the electrodes 33 and 34 is caused. Then, detecting an electric potential of the contact point through the electrode 43 of the upper substrate 22 makes it possible to detect a position of the contact point in the X-axis directions.
On the other hand, if the predetermined voltage of Vcc between the electrodes 43 and 44 formed on the upper substrate 22 is applied, a potential gradient between the electrodes 43 and 44 is caused. Then, detecting an electric potential of the contact point through the electrode 33 or the electrode 34 of the lower substrate 21 makes it possible to detect a position of the contact point in the Y-axis directions.
At this time, the potential gradient between the electrodes 43 and 44 of the upper substrate 22 is different from the potential gradient between the electrodes 33 and 34 on the lower substrate 21. Accordingly, it is possible to perform detection without the resistance of the conductive films 32 or 42 influencing where the electric potential of the contact point is detected. The interface circuit substrate 12 detects a coordinate in the X-axis directions from the electric potential in the X-axis directions, a coordinate in the Y-axis directions from the electric potential in the Y-axis directions, and sends these coordinates to an information process unit 5.
As illustrated in FIG. 1, the touch panel 11 is glued and mounted on the display device 2. According to what is shown on the screen 3 of the display device 2, an operator gives inputs. Thus, it is important to accurately position the touch panel 11 relative to the screen 3 of the display device 2.
The touch panel 11 and the display device 2 have been conventionally positioned by fitting outer shapes of the touch panel 11 and the display device 2. As a result, the relative position of the touch panel 11 to the display device 2 is inaccurate, whereby resulting in poor operation. Thus, it is required that the relative position of the touch panel 11 to the display device 2 be corrected.
Conventionally, the relative position of the touch panel 11 to the display device 2 has been commonly corrected by operator's manipulations. The operator manipulates the input device 1 and others to set the information processing unit 5 in a position correction mode. Once the information processing unit 5 is in the position correction mode, the information processing unit 5 starts to display a position to be depressed on the screen 3 of the display device 2. The operator depresses the position displayed on the display device 2.
Next, the information processing unit 5 detects a position on the touch panel 11 depressed by the operator on the basis of coordinate information from the interface circuit 12.
Then, the information processing unit 5 compares the position to be depressed on the screen 3 of the display device 2 with the position on the touch panel 11 depressed by the operator, and computes a correction value so that the coordinate information from the interface circuit 12 can be consistent with the coordinate information on the position to be depressed on the screen 3 of the display device 2. The information processing unit 5 or the interface circuit 12 saves the correction value. Thereafter, the information processing unit 5 or the interface circuit 12 corrects the coordinate information on the basis of the saved correction value. The information processing unit 5 determines a coordinate on the basis of the coordinate information that has just been corrected according to the correction value.
Under the heretofore-described conventional correction of the relative position of the touch panel 11 to the display device 2, however, operations for correcting the relative position are complicated because of the necessity of operator's manipulations.
On the other hand, the connections between wiring patterns on the touch panel 11 or the touch panel itself and the flexible wiring board 23 deteriorate over time, whereby enlarging the wiring resistance. Under conventional touch panels, however, wiring conditions of the touch panel 11, the flexible wiring board 23 and others have not been taken into consideration. Thus, we have the problem that the precision of the coordinate detection deteriorates over time.